1. Field of the Invention
The present invention relates to a process for manufacturing a circular saw blade by gluing at least two congruent metal blades of an iron-based alloy. The present invention also relates to a circular saw blade obtainable by that process.
2. Discussion of Background Information
One-piece circular saw blades are set in vibration during high-power operation of the saw and, as a result, often cause considerable noise pollution. It is known to achieve a distinct reduction in the emitted airborne noise level by using a sandwich-like structure of the master blade. In this connection, at least two round lateral plates are connected to one another at least in parts thereof, thereby forming a master blade, and cutting tips or cutting segments are arranged circumferentially thereon. Connecting the lateral plates, if necessary via a center plate, can be accomplished metallically, by soldering as well as by spot welding or by gluing.
When joining by gluing, two congruent metallic blades are placed on top of one another with an intermediate layer of a thin adhesive layer placed therebetween, whereafter the adhesive is allowed to harden, in particular, thermally. In doing so, it can be advantageous, as shown by DE 44 05 475, if gluing the parts takes place only in the radial area at a distance from the circumference of the saw blade.
The vibrations of the saw blade that still occur in a muffled manner despite the sandwich structure as well as the changing or pulsating mechanical stresses in a high-performance operation can produce at least partial disintegration of the lateral blades. Studies have shown that, starting from a defect that is often small in terms of area, separations of adhesive from a blade in many cases occur in the area of the half radius of the saw blade, which then enlarge in a conchiform manner and ultimately lead to the drift of the pitch circle of the cutting segments or cutting tips, respectively, in an axial direction during saw operation and/or to the same breaking off from the master blade. As a result, the durability in operation of the individual saw blades may be quite different, which is particularly disadvantageous if several saw blades are mounted on a shaft to generate a cut.
The present invention eliminates the disadvantages of varying durability and/or disintegration of the lateral blades and provides a glued saw blade that has improved service characteristics. More particularly, the invention provides crack initiation-free gluing of at least two metal blades which results in a circular saw master blade with improved rotational accuracy.
In one aspect, the present invention provides a process for the manufacture of a circular saw blade by gluing together at least two congruent metal blades of an iron-based alloy. In this process, at least two circular-saw-shaped metal blades made from heat-treated sheet material of iron-based alloy are provided and partially plastically deformed all around in the area of their half radius. The inner lateral surfaces of the metal blades are treated to provide them with a roughness according to EN ISO 4287 and EN ISO 4288 (DIN 4762) represented by a maximum profile height RZ of about 3.0 to about 7.0 xcexcm and an arithmetic mean roughness index Ra of about 0.30 to about 0.75 xcexcm. An adhesive is applied onto the inner lateral surface of at least one of the metal blades and the metal blades are combined with their inner lateral surfaces facing each other to form a sandwich structure. The adhesive is thermally hardened while applying pressure to the sandwich structure. Additionally, the outer lateral surfaces of the metal blades are treated to provide them with a surface roughness represented by a maximum profile height RZ of about 5 to about 10 xcexcm.
According to another aspect, the saw blade may have slots and/or teeth in the area of its outer circumference and the above process further comprises securing cutting segments (e.g., diamond segments) and/or cutting tips to circumferential surfaces between said slots and/or teeth. The cutting segments and/or cutting tips may be secured by metallic bonding, for example, soldering and/or welding.
According to another aspect of the above process, the adhesive is applied at a thickness of about 0.03 to about 0.06 mm, measured from the center line (m) of the roughness profile of the inner lateral surface.
In yet another aspect, the thermal hardening of the adhesive is carried out in two stages. For example, a first stage of the thermal hardening comprises heating at a temperature ranging from about 50xc2x0 C. to about 70xc2x0 C. and under a pressure ranging from about 1 to about 3 kg/cm2. This first stage may be carried out for about 10 to about 16 minutes. The second stage of the thermal hardening may, for example, comprise heating at a temperature ranging from about 140xc2x0 C. to about 160xc2x0 C. to complete the hardening of the adhesive.
The inner lateral surfaces may be treated to provide the desired roughness either before or after the treatment of the outer lateral surfaces. For example, the outer lateral surfaces may be treated prior to the partial plastic deforming of the metal blades.
According to still another aspect of the process of the present invention, both the inner lateral surfaces and the outer lateral surfaces of the metal blades may independently be treated by circular polishing and/or brush polishing.
According to another aspect of the present process, the metal blades may be made from the heat-treated sheet material by a thermal cutting operation, e.g., by laser cutting.
Furthermore, in another aspect, the metal blades may be subjected to a tempering treatment prior to the partial plastic deforming. The tempering treatment may, for example, be carried out at a temperature ranging from about 380xc2x0 C. to about 480xc2x0 C.
According to another aspect of the present invention, the iron-based alloy may comprise, in weight percent:
the balance being iron and incidental impurities, with the contents of phosphorus and sulfur each not exceeding about 0.03 percent by weight. This is particularly advantageous if the saw blade has slots and/or teeth in the area of its outer circumference and the above process further comprises soldering cutting segments and/or cutting tips to circumferential surfaces between said slots and/or teeth.
According to yet another aspect, the iron-based alloy may comprise, in weight percent:
the balance being iron and incidental impurities, with the contents of phosphorus and sulfur each not exceeding about 0.03 percent by weight. This is particularly advantageous if the saw blade has slots and/or teeth in the area of its outer circumference and the above process further comprises welding (e.g., by laser welding) cutting segments and/or cutting tips to circumferential surfaces between said slots and/or teeth.
In yet another aspect of the process of the present invention, the metal blades are partially plastically deformed by roller-burnishing.
The present invention also provides, in another aspect, a process for the manufacture of a circular saw blade by gluing together at least two congruent metal blades of an iron-based alloy. This process comprises, in the given order:
providing at least two circular-saw-shaped metal blades cut thermally from heat-treated sheet material of iron-based alloy which comprises, besides iron and incidental impurities, at least about 0.18 weight percent C and at least about 0.20 weight percent Cr;
tempering the metal blades at a temperature ranging from about 380xc2x0 C. to about 480xc2x0 C.;
partially plastically deforming the metal blades all around in the area of their half radius by roller-burnishing;
treating the inner lateral surfaces of the metal blades by brush polishing and/or circular polishing to provide them with a roughness according to EN ISO 4287 and EN ISO 4288 (DIN 4762) represented by a maximum profile height RZ of about 3.0 to about 7.0 xcexcm and an arithmetic mean roughness index Ra of about 0.30 to about 0.75 xcexcm;
applying an adhesive onto the inner lateral surface of at least one of the metal blades at a thickness of from about 0.03 to about 0.06 mm, measured from the center line (m) of the roughness profile of the inner lateral surface;
congruently combining the metal blades with their inner lateral surfaces facing each other to form a sandwich structure;
thermally hardening the adhesive by heating it, in a first hardening stage, at a temperature ranging from about 50xc2x0 C. to about 70xc2x0 C. and a pressure ranging from about 1 to about 3 kg/cm2 for a period of about 10 to about 16 minutes, cooling it to ambient temperature, and heating it again, in a second stage, at a temperature ranging from about 140xc2x0 C. to about 160xc2x0 C. to complete the hardening of the adhesive; and
treating the outer lateral surfaces of the metal blades by brush polishing and/or circular polishing to provide them with a surface roughness represented by a maximum profile height RZ of about 5 to about 10 xcexcm.
In this process, the saw blade may have slots and/or teeth in the area of its outer circumference and cutting segments and/or cutting tips may be secured to circumferential surfaces between said slots and/or teeth, e.g., by metallic bonding (such as soldering and/or welding).
In another aspect, the present invention provides a circular saw blade obtainable by the above processes.